Not Applicable
1. Field of the Invention
The invention generally relates to stock material such as light transmissive sheets with gas space between and a sealed edge, such as a double glazed storm window. Similarly, the invention generally relates to static structures such as a composite prefabricated panel including adjunctive means. More specifically, the static structure may have a sandwich or hollow structure with sheet-like facing members, especially parallel transparent panes such as a double glass window panel. The invention also relates to an internal spacer between parallel transparent panes. The static structure may be a hermetically sealed opaque or transparent panel. In a further aspect, the invention generally relates to adhesive bonding and methods for surface bonding and assembly, especially for making a multi-pane glazing unit with air-spaced panes.
2. Description of Related Art Including Information Disclosed Under 37 CFR 1.97 and 1.98
Insulating glazing (xe2x80x9cIGxe2x80x9d) structures include double glazed windows and other multi-pane glazing units. These structures are ubiquitous in modern architectural construction, both residential and commercial, where they are commonly found as windows, glass walls, and doors. A primary technological problem faced by IG units is their low insulating value, relative to many other types of insulated panel and wall structures. In both hot and cold climate conditions, a low insulating value results in energy loss from a building that is either heated or cooled by an energy consuming system, such as a heating system or a cooling system that directly or indirectly consumes fuel. On a broad scale, the challenge presented by IG structures is to reduce energy loss through them and to reduce the resultant higher costs for basic utilities in the buildings using IG structures.
Typically, an IG unit is formed of two or more glass panes, spaced apart by a mechanical spacer to form a central air space or interlayer, and sealed at the peripheral edge of the panes to prevent entry of humidity. In substantially all commercial IG units, the central air space is a dead air space, because the IG unit is sealed as a static unit, with no opportunity for exchange of gas from this central space. Although terms such as xe2x80x9cairxe2x80x9d and xe2x80x9cair spacexe2x80x9d are commonly used in connection with the internal central space of an IG unit, unless context dictates otherwise these terms do not imply that the gas is or should be limited to the mixture commonly referred to as air. As described below, one or more specific gasses other than ordinary air are used to fill the air space. Most commonly the construction of an IG unit is a hermetically sealed glazing assembly in which two similarly sized glass panels, which may be defined as interior and exterior panes, are bonded along their corresponding edges by structural sealants and moisture barriers to opposing surfaces of a central parametric spacer tube. The spacer often is about one-half inch (13 mm) by xe2x85x9c inch (10 mm) thin wall metallic tube, which is perforated and contains a desiccant agent. The central air space is defined by the glass panels and the spacer tube. The central insulating air space is dried by exposure to beads of desiccant stored within the perimeter spacer tube. The tube is perforated and vented to the insulating central air space along its interior parametric surface.
Modifications to this basic design have focused on methods of improving insulating values of sealed glazing assemblies through 1) deposit of a transparently thin metal oxide coating on the surface of exterior glass panes to filter and trap radiant energy; 2) addition of a third glass panel and corresponding second parametric spacer and insulating air space to further constrain thermal conduction through the assembly; 3) introduction of low-conductive gases such as argon and krypton into the central insulating air space, replacing some or all of the normal air with the selected gas; 4) replacement of perforated metallic perimeter spacer tubes with a variety of alternative spacer configurations employing materials exhibiting low thermal conductivity, and 5) various combinations of these methodologies.
As a group, these modifications are passive in that their approach to improving insulating values of sealed glazing assemblies proceed from a common premise. Uniformly, they seek to provide more effective intervening barriers to conduction of temperature extremes through sealed glazing assemblies and into interior living and working quarters. Only the metal oxide coating provides a benefit other than lower thermal conduction rates. Coated glass also reflects certain wave lengths of light while passing other light through to the interior. Metal oxide coatings also create a spectrum of new problems, in that direct sunlight on these coatings causes excessive heating in exterior glass panes and contributes to thermally induced breakage of glass, failure of structural seals, failure of vapor barriers and disintegration of the glazing units due to differing rates of linear expansion of constituent components.
Edge seal systems are an area of considerable research. The spacer can have considerable variation in its design and material of construction. Spacers commonly are formed of aluminum, steel, or polyvinyl chloride. Spacer shapes can be tubular or an open-sided channel. In addition, spacers often contain a desiccant to reduce moisture content of the gas or air in the air space, thus preventing condensation within the IG unit or at least delaying the time period when condensation will occur. Various materials are used as the sealant, with considerable variation in success of keeping out air and humidity. Sometimes the glass panes are held in position by the sealant, while other designs employ an exterior channel or keeper to hold the panes in place.
Energy transmission through the edge portion of an IG unit is well known to be greater than through the dead air space at the center of the unit. The pathway through the edge seal and spacer tends to be much more conductive, with the result that as exterior temperature decreases, the interior surface temperature of an IG unit tends to be significantly lower at the edges. Thus, when moisture is present, condensation starts near the edges and spreads over an entire IG unit as exterior temperature decreases.
The study of energy transmission near the edge of an IG unit is such a significant area that it has gained special recognition as xe2x80x9cwarm-edge technologyxe2x80x9d or xe2x80x9cWET.xe2x80x9d The goal of WET is to enhance both condensation resistance and thermal resistance at the perimeter of the IG unit, particularly in the 63 mm (2.5 inches) above the sight line of the IG perimeter. While studies are concentrated on this perimeter area as the initially effected area, studies confirm that temperature changes begin at the edge of an IG unit and continue toward the center of the glass until the change reaches the center. Thus, the 63 mm perimeter is an area of primary concern, although the effects concern the entire IG unit.
Studies with spacer bars of different thermal conductivity have shown that the temperature of the glass surface on the warm side of an IG unit increases with the thermal resistance of the spacer bar material. Thus, many improvements in construction of IG units have focused upon the material and design of the spacer in order to increase thermal resistance.
Commercial, industry standard, dual pane insulated glazing units with metallic spacer tubes, as widely manufactured according to present practices, have predictable properties. This type of industry-standard product will be referred to as the conventional product. The conventional window provides thermal insulating properties that are sufficient for the intended use when exterior temperatures are of a moderate range, such as greater than 35xc2x0 F. (1.67xc2x0 C.) and less than 85xc2x0 F. (29.44xc2x0 C.). Relatively more extreme exterior temperatures, outside the defined moderate range, overwhelm the thermal insulating properties of the conventional dual pane window and door products. The results are excessive interlayer heat flux, a consequential loss of living-space comfort, condensation of water vapor on interior glass, ice formation on interior glass, and substantially higher heating and cooling costs.
Insulated glazing units are comprised of various materials each having a characteristic rate of thermal conductivity. As a practical matter, perimeter metallic spacer tubes serve as a thermal bridge in conventional insulated glazing units. Dual glass panes and interlayer air have respective thermal conductivity of 0.5971 Btu/hour-foot-degree F. (1.033 Watts/(Meter-degree K)) and 0.0139 Btu/hour-foot-degree F. (0.0139 Watts/(Meter-degree K)), while aluminum and steel spacer tubes have respective thermal conductivity of 135 Btu/hour-foot-degree F. (233 Watts/Meter-degree K)) and 11.2 Btu/hour-foot-degree F. (19.376 Watts/Meter-degree K)).
With the exception of coated glass and certain external heat exchange devices, prior methods for suppressing heat flux in insulating glass have focused on replacing highly conductive constituent materials with other materials that are less efficient thermal conductors. While there is strong need and desire to improve the insulating characteristics of multi-pane glazing units, little apparent consideration has been given to eliminating temperature gradients, formed across the interlayer, as an alternative method of suppressing interlayer heat flux. In some cases, thermal efficiency of an IG assembly has been improved by using low conducting materials. However, certain negative consequences attend the use of such alternate materials, including a relative high cost of low conduction materials, a significant loss of manufacturing productivity, and substantial constraints on IG unit size and shape.
The problems of heat flux at the edges of IG units are somewhat similar to problems in hollow aluminum or steel sash and framing components of certain window and door assemblies. The poor insulating characteristics of aluminum window and door framing systems have driven many window manufacturers to adopt PVC or composite alternatives in place of aluminum extrusions.
However, an exception to this trend to use PVC and composite is found with fabricators of curtain-wall window and door systems most commonly seen in large scale architectural projects. The low cost, strength and durability of aluminum window and door framing systems in such construction projects apparently outweigh insulating inefficiencies. Nonetheless, energy costs drive the specification of coated glass IG units for these projects to achieve lower operating costs. This apparent conflict in efficiencies can be better understood by an explanation of a measurement standard known as xe2x80x9cU-value,xe2x80x9d which often is used in specifying curtain wall systems. U-values measure insulating efficiency at the center-of-panel rather than at the critical edge area. The U-value specification standard largely ignores the relative inefficiency of aluminum framing in curtain wall systems.
Two patents have suggested benefits in heating windows in automobiles, although neither addresses reducing thermal conductivity nor increasing condensation resistance. Both suggest warming the interlayer of a double layer automobile windshield. U.S. Pat. No. 6,066,372 to Miles proposes placing a reservoir of anti-freeze solution at the base of the windshield. U.S. Pat. No. 3,807,791 to Boyer warms the interlayer with an electrical resistance heater in the edge seal of the windshield.
Windows in architectural structures have been externally heated or cooled in various ways. German Patent 40 24 143 to Koester circulates a heating or cooling fluid from an external heat exchanger through the spacer between panes. German Patent 197 44 423 to Loewe pumps a heated or cooled fluid, which may be water, around a door or window. U.S. Pat. No. 4,155,205 to Polman controls condensation by placing a heat conductive metal rod in communication between the interlayer and outside weather. The rod serves as a cold spot that preferentially condenses moisture. U.S. Pat. No. 5,087,489 to Lingemann proposes an IG unit with electrical resistance elements deposited on the inside face of one pane, and with a two part spacer having an insulating urethane center strip for low thermal conductivity between the heated and unheated panes.
An IG unit can be used as part of a solar collector, although the solar collector art is qualified and limited by the need for the collector to face the sun. Such technical issues as reducing thermal conductivity or increasing condensation resistance at the edge of an IG unit can be relevant to solar collectors as well as to architectural applications. However, the technical solutions are not universally applicable to both applications if they rely on solar-related attributes, since many architectural IG units do not face the sun.
A representative solar collector using an IG unit is U.S. Pat. No. 2,595,905 to solar pioneer M. Telkes, in which an IG unit serves as a front wall that transmits sunlight to a separate collector cell filled with phase change material. The cell is bordered with venetian blinds for directing input and radiation of collected heat. Other patents placing a window in front of a collector cell include U.S. Pat. No. 4,739,748 to Stice and U.S. Pat. No. 4,421,101 to Stice. U.S. Pat. No. 4,412,528 to Elzinga uses a single pane of glass with mirrored edges to direct solar radiation into a heat storage reservoir filled with phase change material (xe2x80x9cPCMxe2x80x9d).
Phase change materials (xe2x80x9cPCMsxe2x80x9d) are known for their thermal storage properties in solar collectors. They have found special utilization in window structures by changing opacity. U.S. Pat. No. 4,532,917 to Taff et al. discloses filling the interlayer with a PCM that shifts from transparent to translucent with dropping temperature, thereby increasing solar absorption. Achieving a similar result, an IG unit according to U.S. Pat. No. 6,001,487 to Ladang is electrically actuated to change the opaque quality of a glass pane coated with electrochromic material.
Certain of these patents appear to have notable deficiencies and limitations. This seems evident, for example, in those that would substitute one source of energy loss with another, such as those supplying external energy into an interlayer in order, supposedly, to reduce energy loss from within the living spaces of a building. Whether the net loss is different, after both sources of energy have been considered, seems questionable. The concept of windows plumbed for circulating fluids or electricity also creates new burdens on building construction. IG units that change opacity in order to change their solar absorption perhaps are effective if used on those limited numbers of walls exposed to sunlight, but the altered opacity degrades or sacrifices the viewing quality of the window. Thus, many of the suggested concepts are of little use or unlikely to be accepted for commercial and architectural applications.
A highly desirable improvement in IG units and structures would be a means for reducing energy transmission that operates passively and without a need for external plumbing, additions or alterations to the general structure and viewing function of an IG unit. Such an improvement would be adaptable to the countless buildings already in existence without modification other than the one-for-one replacement of IG units. Further, it would be desirable to reduce heat flux through metal framing and sash members by using similar methods to reduce temperature gradients.
To achieve the foregoing and other objects and in accordance with the purpose of the present invention, as embodied and broadly described herein, the insulated glazing structure and method of operation of this invention may comprise the following.
Against the described background, it is therefore a general object of the invention to provide an improved apparatus and method for suppressing heat flux in insulating glazing products. Such suppression of heat flux is preferred to be through characteristics of the materials incorporated into the IG structure, acting in response to rising or falling temperature on one face of the structure.
The IG structure employs an un-vented, thermally conductive, hermetically sealed spacer element containing phase change material (PCM). Such spacer is located in an interlayer between spaced, parallel sheets of glazing, such as in double glass window panels, especially in such panels having a metal oxide coating on the exterior pane. The phase change material, by its inherent ability to absorb and release heat, suppresses or delays temperature differentials within a dual-glazed panel. Avoiding extreme temperature flux is helpful in preserving moisture barriers, preserving structural seals, and avoiding heat induced glass breakage.
Another object is to improve the effective range of IG units from their present moderate range of about 30xc2x0 F. (xe2x88x921.1xc2x0 C.) to 85xc2x0 F. (29.4xc2x0 C.). More extreme exterior temperatures overwhelm the thermal insulating properties of conventional dual pane window and door products. The result is excessive interlayer heat flux and significant loss of living-space comfort. Other effects can include condensation of water vapor on interior glass, ice formation on interior glass and substantially higher heating/cooling costs. These effects can be avoided by suppressing heat flux over an improved range of temperatures.
Still another object is to provide a technology for suppressing heat flux, adaptable to metal framing and sash members as often used in architectural curtain-wall structures.
The effects of extreme exterior temperatures are conducted most readily through an insulated glazing unit at the perimeter spacer, which is at the edge of glass. Therefore, an important object is to moderate the edge effects by a strategically positioning a phase change material (PCM) in a parametric reservoir around the interlayer. The PCM undergoes a phase transition to produce a spontaneous transfer of heat when triggered by a temperature gradient that spans the phase transition temperature of the PCM.
Another object is to provide adequate latent heat capacity for effective control of interlayer heat flux. A phase change material in a parametric reservoir should provide an in-place density greater than 7.0 grams of paraffinic oil PCM per cubic inch volume of sealed parametric reservoir (114.8 grams PCM/milliliter of reservoir). In addition, the reservoir should have at least a 0.06 square inch (38.7 square millimeter) enclosed profile area.
A further object of the invention is to maximize the duration of latent heat exchange with the interior field glass pane during phase transition. This can be achieved through use of high shoulder sealed perimeter reservoir tubes.
Additional objects, advantages and novel features of the invention shall be set forth in part in the description that follows, and in part will become apparent to those skilled in the art upon examination of the following or may be learned by the practice of the invention. The object and the advantages of the invention may be realized and attained by means of the instrumentalities and in combinations particularly pointed out in the appended claims.
According to one aspect of the invention, an improved glazing assembly is formed of at least first and second juxtaposed glazed panes. An interlayer separates the panes and contains a gas. The edges of the panes are closed by a seal. The improvement is a thermally conductive, hermetically sealed receptacle positioned between the panes and containing a phase change material (PCM). The PCM contained within the receptacle reversibly absorbs, stores, and releases heat in response to a temperature change applied at least at one pane of the glazing assembly.
Another aspect of the invention is a method of suppressing heat flux due to a temperature gradient applied between juxtaposed panels of a multi-panel structure formed of at least an inner panel and a juxtaposed outer panel, separated from each other by an interlayer. A first step is providing a closed reservoir between the inner and outer panels and in communication with the interlayer. A second step is providing within the closed reservoir a resident phase change material having a transition temperature within the temperature gradient. A third step is suppressing interlayer heat flux by establishing a transient plane of near temperature equilibrium within the resident phase change material of the reservoir.
The accompanying drawings, which are incorporated in and form a part of the specification illustrate preferred embodiments of the present invention, and together with the description, serve to explain the principles of the invention. In the drawings: